The usual hot wire TCD (thermal conductivity detector) comprises a metallic block containing one or more cylindrical cavities through which the gas stream under test flows. A heated element, notably an electrically heated resistance wire positioned inside the cavity, looses heat to the block at a rate depending upon the thermal conductivity of the gas therein, which in turn changes wire temperature and wire resistance. The changes in wire resistance are measured.
The TCD is a concentration dependent system, and if the gas volume containing a GC component is increased after leaving the GC column through dilution of the component in more carrier gas, the reduced concentration of component due to such band broadening detrimentally affects the TCD system. Unfortunately passage of gas through the detector itself introduces variences that contribute to the band broadening effect.
A detailed discussion of the variances attributable to cell volume and cell design has been provided concurrently with the genesis of this invention by Lochmuller et al. in J. of Chromatographic Science, Vol. 15, pp. 285-289, (August 1977).